The use of color-forming coupler compounds which react with the development product of primary aromatic amino developing agents to form colored images upon photographic development is well known and has been the subject of many patents and other publications. The dyes formed in this way are usually insoluble in water and in the ordinary development and fixing solutions. Such coupler compounds may conventionally be added to the development solutions, or they may be incorporated into the photographic layers during the manufacture of the light sensitive elements. In this latter instance, the coupler compounds are referred to as "incorporated couplers." Incorporated couplers usually remain essentially immobile in their respective layer of the photographic element due largely to the fact that their molecules are fairly large. Immobile incorporated color-forming coupler compounds usually contain at least one so-called "ballasting" group in their molecule. Such "ballasted" photographic couplers are well known in the art and need not be dealt with in detail at this point. It should be understood that the incorporated couplers referred to herein are of the ballasted type.
Color-forming coupler compounds are generally used for subtractive color photography. Upon color development they form yellow, magenta or cyan dyes. For several important and well-known reasons, subtractive color photographic elements which are designed for realistic color rendition contain at least three distinct layers coated on a photographic support such or a transparent polymeric sheet. Generally, cyan-forming materials are placed in the color layer nearest the support, the silver halide in that layer being specially sensitized to the red region of the visible spectrum. In a color layer over the red-sensitized layer just described (possibly separated from that layer by one or more additional special purpose layers) is usually placed in magenta-forming layer, into which is incorporated magenta-forming color couplers. The silver halide in this magenta-forming layer is specially sensitized to the green region of the visible spectrum. In a third color-forming layer, which is coated over the green-sensitized layer (usually with a blue-light-absorbing layer between them) are incorporated yellow-forming coupler compounds. This yellow layer contains silver halide that is sensitive essentially to only the blue region of the visible spectrum.
Over the years, color photographic technology has been advanced and refined to the point that significant improvements are difficult to obtain. Meanwhile, consumers of color photographic products continue to demand products having better properties. Typical of the properties of concern to consumers are those directed to the clarity, sharpness and granularity of the final photographic product; i.e., the color photograph or transparency.
It is generally known that in order to decrease the granularity of the image, a larger number of silver halide grains should be used (U.S. Pat. No. 2,689,793). The grains should not be reduced in size because of the need to maintain the photographic speed or sensitivity of the element. Thus, by increasing the number of silver halide grains (to improve granularity), one must increase the relative amount of silver halide in each layer. Since increases in the silver halide content of a layer generally cause concomitant increases in dye density (in each of the color layers) photographic products could result from using this approach (more silver halide) which have color densities that are too high. This, of course, would be undesirable.
One method of overcoming the problems caused by too much color density (which problems are of concern mainly in the magenta and cyan layers of the photographic element), is to use a so-called "competing coupler" during the development of the element. The competing coupler preferably forms either a colorless compound upon its reaction with oxidized color developer, or a dye which is soluble in the developer solution and can be removed by rinsing the developed element. The type and amount of competing coupler may be chosen so that the undesirable increase in color density in the magenta and cyan layers referred to above does not occur.
A complication in our problem must be considered at this point. It is apparent that in order to observe the improved granularity described above (which improvement relates almost exclusively to the appearance of the magenta and cyan layers) while at least maintaining good sharpness one should not increase the amount of silver halide in the top (yellow) color-forming layer. This is because the silver halide grains in the yellow color-forming layer deflect and/or scatter the green and red light that passes through the "yellow" dye layer to such an extent that the desired objectives (of retaining excellent clarity and sharpness and improving granularity in the magenta and cyan layers) would not result if one increases the silver halide content of the yellow dye layer to any great extent. However, by using only relatively low levels of silver halide in the yellow dye layer, the use of relatively large amounts of competing couplers (as described above) would be expected to cause an unacceptable loss of yellow color from the yellow dye layer.
It is an object of the present invention to overcome the apparent dilemma described above, so that one can obtain subtractive color photographic products which (i) exhibit the improved granularity characteristics described above (ii) have magenta and cyan dye levels which are not too high, and (iii) have yellow dye levels which are not too low. Thus, the resulting photographic color products also exhibit excellent color fidelity.